1. Field of the Invention
The invention relates to an electroluminescent device, and more particularly, to a host material of the luminescent layer and a hole-blocking material of the electroluminescent device.
2. Description of the Prior Art
In recent history, displays having the characteristics of light weight and high performance, such as liquid crystal displays have become increasingly popular. Nevertheless, problems including narrow viewing angle and slow response rate are still found in most liquid crystal displays, therefore the LCD can not use for displaying high speed moving pictures. The requirement for the backlight of LCD will cause more power consumption. Moreover, the fabrication of large-scale liquid crystal display panels is still difficult to achieve.
Consequently, organic electroluminescent displays have been developed to overcome the aforementioned disadvantage of liquid crystal displays.
In general, organic electroluminescent displays are devices utilizing the property of organic luminescent materials to generate light. An organic electroluminescent device is primarily composed of a pair of electrodes and an organic luminescent layer. The organic luminescent layer includes luminescent materials. When a current passes through a transparent anode and metallic cathode of the device, electrons and holes within the luminescent material will combine and generate exciton, thereby inducing the luminescent material to illuminate and produce light.
However, some problems are found in most organic electroluminescent devices today. Problems arising are especially related to the stability and efficiency of the luminescent material. Recently, luminescent materials used in electroluminescent devices to fabricate the luminescent layer include a host material of tris(8-quinolinol)aluminum (AlQ3) and a doped guest material of a fluorescent material, or a host material of 4,4′-N,N′-dicarbazole-biphenyl (CBP) and a doped guest material of a phosphorescent material. The luminance efficiency is generally higher when utilizing a doped guest material of phosphorescent material than when utilizing the fluorescent material. However, the CBP being utilized will easily induce a crystallization phenomenon, in which the phenomenon will not only reduce the brightness of the electroluminescent device, but also significantly shorten the life expectancy of the device.